The present invention relates to an array substrate used for a liquid crystal display element, and particularly for a liquid crystal display element of in-plane switching type, a liquid crystal display element provided with the array substrate, and a method of manufacturing an array substrate.
In recent years, a display element having a large capacity and a high density which can be used for TV display and graphic display has been eagerly developed and practiced as a display element using liquid crystal. In particular, development and commercial production has been widely made of a liquid crystal display element of an active matrix type capable of displaying an image at a high contrast ratio without cross-talk.
Also, in recent years, a wider view angle has been required for a liquid crystal display element aimed for monitor use, and various techniques for wide view angle has been developed. Particular attention is being paid to a so-called IPS (In-Plane Switching) method in which display pixel electrodes and opposite electrodes are formed on one same substrate and liquid crystal is made respond by an electric field generated substantially in parallel to the substrate.
As a liquid crystal display element of an active matrix type adopting the IPS method, there is proposed a display element in which the display pixel electrodes and opposite electrodes are respectively made of display signal line layers and scanning signal line layers, a supplemental capacity is formed on opposite signal lines, and a thin film transistor (hereinafter referred to as only TFT) of a stagger type is used as a switching element.
Specifically, according to this liquid crystal display element, a MoW film is formed at 200 angstrom on an insulating substrate, scanning signal lines including gate electrodes and opposite signal lines parallel thereto are processed by photoetching thereafter, and the opposite electrodes extending perpendicularly from the opposite signal lines are processed into a predetermined shape. Next, pattern inspection of scanning signal lines is carried out. Thereafter, an insulating film made of SiO with a thickness of 3000 angstrom and i-type amorphous silicon (hereinafter referred to as a-Si) film with a thickness of 500 angstrom serving as a semiconductor layer constituting channel regions for the TFTs are each formed on the entire surface of the substrate by a CVD (Chemical Vapor Deposition) method.
Subsequently, an etching protection film made of SiN for protecting channels of the TFTs is formed at 2000 angstrom also by the CVD method, and thereafter, only the protection film is processed into a predetermined shape by photoetching. Further, an n+ type a-Si film is formed at 500 angstrom by the CVD method, and then, the i-type a-Si film and the n+ type a-Si film are processed into a predetermined shape by photoetching. Subsequently, power supply electrodes for the scanning signal lines and opposite signal lines are processed into a predetermined shape by photoetching.
Next, a Al film is formed at 3000 angstrom by a sputtering, and thereafter, display signal lines, source and drain electrodes of the TFTs, display pixel electrodes, supplemental capacity electrodes, power supply lines of the opposite signal lines, and the n+ type a-Si film between the source and drain electrodes are processed into predetermined shapes. In this case, the display pixel electrodes are arranged in parallel with the opposite electrodes.
Then, a protection film made of SiN is formed at 2000 angstrom by the CVD method and are processed into predetermined shape. A substrate for a liquid crystal display element of an active matrix type (hereinafter referred to as an array substrate) is thus prepared. This array substrate and an opposite substrate made of an insulating substrate are adhered together on each other with a predetermined gap, and a liquid crystal layer is sealed between these substrates, thus completing a liquid crystal display element of an active matrix type.
In the above-mentioned liquid crystal display element of an active matrix type adopting the IPS method, each pixel is constituted by a plurality of apertures interposed between a plurality of substantially linear display pixel electrodes and a plurality of substantially linear opposite electrodes, which are formed of different layers on the same substrate, by means of independent photoetching steps. Therefore, there is a case that the distance between the display pixel electrodes and the opposite electrodes is not uniform in the pixels due to misalignment of patterns during exposure.
For example, if each pixel region includes two display pixel electrodes parallel to each other and one opposite electrode arranged in parallel between the display pixel electrodes, the distances between the opposite electrode and the display pixel electrodes do not become uniform due to misalignment during exposure. In this case, the electric field generated between both electrodes is strong at the portion where the distance between both electrodes is short than at the portion where the distance between both electrodes is wide. Consequently, the responsibility of liquid crystal differs between both portions so that the luminance does not become uniform in one same pixel. This ununiformity in the pixel deteriorates the display quality of the screen and is observed as roughness with eyes.
Meanwhile, in consideration of the responsibility of liquid crystal, the electric field generated between the display electrodes and the opposite electrode should desirably be perfectly parallel to the surface of the array substrate. In practice, however, the electric field becomes arc-shaped due to electrode end effects. Therefore, the effective horizontal electric field between the electrodes is weaker and the responsibility of liquid crystal is lowered than in the case where the electric field is perfectly parallel to the substrate.
Narrowing of the distance between both electrodes can be considered to be a method of compensating the weakening of the electric field. In this case, the numerical aperture is lowered so that the permeability is deteriorated. If the back-light is strengthened to compensate this deterioration, increase of the power consumption is caused undesirably.
Increase of the voltage applied to both electrodes can be considered as another method. This means increase of the drive voltage and leads to increase of the power consumption.
Also, this kind of liquid crystal display element comprises an opposite substrate opposed to the array substrate. A black matrix as a light shielding layer, a color filter, and the like are formed on the opposite substrate. In general, the black matrix is arranged such that the opening portions thereof are opposed to the pixel region of the array substrate, respectively, and the periphery of each opening is layered over the opposed electrode.
However, if the peripheral edges of the openings of the black matrix are positioned between the opposite electrodes and the pixel electrodes due to a relative positional offset between the array substrate and the opposite substrate during assembly, the aperture ratio of the liquid crystal display element is lowered so that the screen luminance is lowered. Inversely, if the peripheral edges of the openings of the black matrix are positioned between the opposite electrodes and the display signal lines, light leaks so that roughness appears on the screen and the contrast is lowered, resulting in deterioration of the image quality. As a method of preventing this positional offset of the black matrix, the width of the opposite electrodes may be thickened. In this case, however, the aperture ratio is lowered.
The present invention has been contrived in consideration of the above circumstances and its object is to provide an array substrate for a liquid crystal element, which is capable of improving the image quality and the response of liquid crystal without increasing the power consumption, a liquid crystal display element comprising the array substrate, and a method of manufacturing the array substrate.
To achieve the above object, an array substrate for a liquid crystal display element according to the present invention comprises: a substrate; a plurality of scanning signal lines and opposite signal lines arranged on the substrate and extending in parallel with each other; a plurality of parallel display signal lines arranged on the scanning signal lines and the opposite signal lines, with an insulating film interposed therebetween, and extending in a direction crossing the scanning signal lines and opposite signal line; and a plurality of pixel regions defined by regions surrounded by the scanning signal lines and display signal lines, respectively.
Each of the pixel regions includes an elongated first electrode having an end which is layered over one of the opposite signal lines so as to constitute a supplemental capacity and another end electrically connected to a crossing portion between one of the scanning signal lines and one of the display signal lines, through a switching element, and a second electrode extending substantially in parallel with the first electrode and having an end electrically connected to the opposite signal line. The first and second electrodes are formed by processing one same conductive layer.
According to an array substrate for a liquid crystal display element according to the present invention, the first and second electrodes are formed by processing the same conductive layer as that constituting the display signal lines.
Moreover, according to an array substrate according to the present invention, the first and second electrodes are formed of a film having a thickness of 3000 angstrom or more or preferably a thickness of 5000 angstrom or more.
Further, according to an array substrate for a liquid crystal display element according to the present invention, each of the first and second electrodes have side surfaces inclined at 30xc2x0 to 90xc2x0 with respect to the surface of the insulating substrate.
Meanwhile, a liquid crystal display element according to the present invention comprises first and second substrates opposed to each other with a liquid crystal layer inserted therebetween, wherein the first substrate includes a plurality of scanning signal lines and opposite signal lines arranged on an insulating substrate and extending in parallel with each other, a plurality of parallel display signal lines arranged on the scanning signal lines and the opposite signal lines, with an insulating film inserted therebetween, and extending in a direction crossing the scanning signal lines and opposite signal lines, and a plurality of pixel regions defined by regions surrounded by the scanning signal lines and display signal lines, respectively.
Each of the pixel regions includes an elongated first electrode having an end which is layered over one of the opposite signal lines so as to constitute a supplemental capacity and another end electrically connected to a crossing portion between one of the scanning signal lines and one of the display signal lines, through a switching element, and a second electrode extending substantially in parallel with the first electrode and having an end electrically connected to the opposite signal line. The first and second electrodes are formed by processing one same conductive layer.
According to the array substrate for a liquid crystal display element and the liquid crystal display element comprising the substrate, the first electrodes which function as display pixel electrodes and the second electrodes which function as opposite electrodes are formed by photo-etching one same conductive layer in one same step. Therefore, the distance between both kinds of electrodes can be uniform over the entire surface of the substrate. Accordingly, the electric fields generated between both kinds of electrodes can be uniform so that the response of liquid crystal is uniform at any of the pixel regions over the display area. As a result, roughness of the screen is reduced and the image quality of the liquid crystal display element is improved.
In addition, if the first and second electrodes are thickened to 3000 angstrom or more while the distance between the opposite substrate and the first substrate having the first and second electrodes is maintained to be constant, the ratio of liquid crystal which responds to the electric fields generated between the side surfaces of both kinds of electrodes and in substantial parallel with the surface of the insulating substrate is increased. Further, since the direction of the electric field generated from the surface of conductive material is perpendicular to the surface of the conductive material, the electric fields between the side surfaces of both kinds of electrodes can be more parallel to the surface of the insulating substrate if the inclination angle of the side surfaces of the electrodes to the surface of the insulating substrate is enlarged. Particularly, in a case where the inclination angle is 90xc2x0 to the surface of the insulating substrate, the electric fields generated between the side surfaces of the first and second electrodes are parallel to the surface of the insulating substrate and the intensity of the electric fields can be maximized if the distance between both electrodes or the drive voltage is constant. Accordingly, the response of liquid crystal can be improved without increasing the power consumption.
Meanwhile, an array substrate for a liquid crystal display element according to the present invention comprises: a plurality of scanning signal lines and opposite signal lines arranged on an insulating substrate and extending in parallel with each other, a plurality of parallel display signal lines arranged on the scanning signal lines and the opposite signal lines, with an insulating film inserted therebetween, and extending in a direction crossing the scanning signal lines and opposite signal lines, and a plurality of pixel regions defined by regions surrounded by the scanning signal lines and display signal lines, respectively.
In each of the pixel regions, there are provided an elongated first electrode electrically connected to a crossing portion between one of the scanning signal lines and one of the display signal lines, through a switching element, an elongated second electrode extending substantially in parallel with the first electrode and electrically connected to the opposite signal line, and an elongated light shielding layer positioned below the second electrode adjacent to the display signal line, with an insulating film interposed therebetween, and extending substantially in parallel with the second electrode to shield a gap between the display signal line and the second electrode. The first and second electrodes are formed by processing one same conductive layer.
Also, according to the present invention, the light shielding layer includes a side edge portion positioned to be layered over the second electrode with the insulating film interposed therebetween.
In addition, the display signal lines and the first and second electrodes are formed by processing one same conductive layer having a light shielding characteristic.
Further, the display signal lines and the first and second electrodes are provided on the insulating film, and the second electrode is electrically connected to the opposite signal line through a contact hole formed in the insulating film.
A liquid crystal display element according to the present invention comprises first and second substrates arranged to be opposed to each other with a liquid crystal layer interposed therebetween, wherein the first substrate includes a plurality of scanning signal lines and opposite signal lines arranged in parallel with one another on an insulating substrate, a plurality of display signal lines arranged in parallel with each other on the scanning signal lines and the opposite signal lines, with an insulating film interposed therebetween, such that the display signal lines cross the scanning signal lines and opposite signal lines, and a plurality of pixel regions defined by regions surrounded by the scanning signal lines and display signal lines, respectively.
In each of the pixel regions, there are provided an elongated first electrode electrically connected to a crossing portion between one of the scanning signal lines and one of the display signal lines, through a switching element, an elongated second electrode extending substantially in parallel with the first electrode and having an end electrically connected to the opposite signal line, and an elongated light shielding layer positioned below the second electrode adjacent to the display signal line, with the insulating film interposed therebetween, and extending substantially in parallel with the second electrode thereby to shield a gap between the display signal line and the second electrode. The first and second electrodes are formed by processing one same conductive layer.
According to the array substrate constructed as described above and the liquid crystal display element comprising the substrate, the first electrodes and the second electrodes are formed by photo-etching a common conductive layer in one same step. Therefore, the distance between both kinds of electrodes:can be uniform over the entire surface of the first substrate. Accordingly, the electric fields generated between both kinds of electrodes can be uniform over the entire surface of the first substrate, so that the response of liquid crystal are uniform at any of the opening portions respectively constituting pixels, over the entire surface of the display area. As a result, the roughness of the screen is reduced and the display quality of the liquid crystal display apparatus is improved.
Also, an elongated light shielding layer is provided as a lower layer below the second electrode adjacent to the display signal line and extends substantially in parallel with the second electrode. The shielding layer shields the gap between the display signal line and the second electrode. Therefore, while electrically insulating the first and second electrodes, the width of the light shielding region can be enlarged without lowering the aperture ratio of the pixel region. Accordingly, even if a positional offset appears more or less between the array substrate and the second substrate during assembly of the liquid crystal display element, the side edges of the opening of the light shielding layer on the second substrate side can be securely positioned to oppose the light shielding region of the array substrate. As a result of this, neither the aperture ratio nor the luminance of the liquid crystal display element is lowered. The power consumption of the back light is not required to compensate for such lowering of the aperture ratio or luminance, and leakage of light caused by a positional offset can be prevented. In this manner, it is possible to provide a liquid crystal display element with excellent display quality.
Further, an array substrate according to the present invention comprises: a substrate; a plurality of scanning signal lines arranged on the substrate and extending in parallel with each other; a plurality of opposite signal lines arranged on the substrate to extend in parallel with the scanning signal lines, each of the opposite signal lines being located substantially at a center between two adjacent scanning signal lines; a plurality of display signal lines arranged in parallel with each other on the scanning signal lines and the opposite signal lines, with an insulating film interposed therebetween, on the substrate, such that the display signal lines cross the scanning signal lines and opposite signal line; and a plurality of pixel regions defined by regions surrounded by the scanning signal lines and the display signal lines, respectively.
Each of the pixel regions includes a first electrode electrically connected to a crossing portion between one of the scanning signal lines and one of the display signal lines, through a switching element, and a second electrode which is formed of one same conductive layer as that constituting the first electrode and arranged in parallel with the first electrode with a predetermined interval therebetween, the second electrode being electrically connected to the opposite signal line.
Also, an array substrate for a liquid crystal display element according to the present invention comprises: a substrate; a plurality of scanning signal lines arranged in parallel with each other on the substrate; a plurality of opposite signal lines provided on the substrate to extend in parallel with the scanning signal lines and respectively arranged apart from the scanning signal lines by a predetermined distance; a plurality of display signal lines arranged in parallel with each other on the scanning signal lines and the opposite signal lines, with an insulating film interposed therebetween, on the substrate, such that the display signal lines cross the scanning signal lines and opposite signal line; and a plurality of pixel regions defined by regions surrounded by the scanning signal lines and the display signal lines, respectively.
Each of the pixel regions includes a first electrode electrically connected to a crossing portion between one of the scanning signal lines and one of the display signal lines, through a switching element, a second electrode which is formed of one same conductive layer as that constituting the first electrode, arranged in parallel with the first electrode with a predetermined interval therebetween, and electrically connected to the opposite signal line, and an opening portion formed in the insulating film between the opposite signal line and one of the scanning signal lines adjacent to the opposite signal line and extending to a surface of the substrate.
Further, a manufacturing method according to the present invention comprises:
forming a plurality of scanning signal lines and opposite signal lines in parallel with each other, on an insulating substrate, and forming an insulating film layered over the scanning signal lines and opposite signal lines;
forming a plurality of display signal lines in parallel with each other on the insulating film such that the display signal lines cross the scanning signal lines and opposite signal line; and
patterning a common conductive layer formed on the insulating film, thereby to form an elongated first electrode having a first end which is layered over one of the opposite signal lines so as to constitute a supplemental capacity and another end electrically connected to a crossing portion between one of the scanning signal lines and one of the display signal lines, through a switching element, and a second electrode extending substantially in parallel with the first electrode and electrically connected to the opposite signal line, in each of a plurality of pixel regions defined by regions surrounded by the scanning signal lines and display signal lines, respectively.
Further, according to a method of the present invention, a first metal film formed on the insulating substrate is patterned to form the scanning signal lines and opposite signal lines, and a second metal film formed on the insulating film is patterned to form the display signal lines, and the first and second electrodes.
Moreover, a method of manufacturing an array substrate for a liquid crystal display element, according to the present invention, comprises:
forming a plurality of scanning signal lines in parallel with each other on an insulating substrate;
forming a plurality of opposite signal lines on the insulating substrate so as to extend in parallel with the scanning signal lines and each to be arranged substantially at a center between two adjacent scanning signal lines;
forming an insulating film covering the scanning signal lines and opposite signal lines on the insulating substrate;
forming switching elements using the scanning signal lines as control terminals, on the insulating substrate;
forming contact holes at those positions of the insulating film which are opposed to the opposite signal lines;
forming a plurality of parallel display signal lines on the insulating substrate so as to extend in a direction in which the display signal lines cross the scanning signal lines and the opposite signal lines and to be connected to input terminals of the switching elements; and
forming on the insulating film a first electrode connected to an output terminal of one of the switching elements and a second electrode connected to one of the opposite signal lines through the contact hole, in each of pixel regions defined by regions surrounded by the scanning signal lines and the display signal lines, respectively.
Further, a method of manufacturing an array substrate for a liquid crystal display element, according to the present invention, comprises:
forming a plurality of scanning signal lines in parallel with each other on an insulating substrate;
forming a plurality of opposite signal lines on the insulating substrate so as to extend in parallel with the scanning signal lines with a predetermined interval therebetween;
forming an insulating film covering the scanning signal lines and opposite signal lines on the insulating substrate;
forming switching elements using the scanning signal lines as control terminals, on the insulating substrate;
forming opening portions at those portion of the insulating film which are located between the scanning signal lines and the opposite signal lines;
forming contact holes at those positions of the insulating film which are opposed to the opposite signal lines;
forming a plurality of parallel display signal lines on the insulating substrate so as to extend in a direction in which the display signal lines cross the scanning signal lines and the opposite signal lines and to be connected to input terminals of the switching elements; and
forming on the insulating film a first electrode connected to an output terminal of one of the switching elements and a second electrode connected to one of the opposite signal lines through the contact hole, in each of pixel regions defined by regions surrounded by the scanning signal lines and the display signal lines, respectively.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.